1. Field of the Invention
The present invention relates to a generator of very high voltage, and high current pulses.
2. Description of the Related Art
This invention is used in the supply of very high power klystrons and certain electron tubes, such as free electron lasers. This invention can also be used in the field of flash radiography or ionization. This invention can also constitute a polarization source in accelerators using collectors for recovering the energy of very intense electron beans (from a hundred to a few thousand amperes).
In such applications, the requisite pulses are very high voltage rectangular pulses (above 500 kV), supplied under an impedance of 500 to 3000 ohms and having the shortest possible rise time and the flattest possible amplitude plateau, with a duration of 100 nanoseconds to a few microseconds.
In existing generators, also known as modulators, use is generally made of a low impedance formation line constituted by discreet components (capacitors and inductances). A high voltage thyratron controls the discharge of the line. The operating voltage of the thyratrons does not exceed 60 kV, so that a step-up transformer has to be used. As a result of the necessary electrical insulation associated by increasing the high voltage, said transformer necessarily has significant magnetic leaks, which limits the rise; time of the output pulse. At 500 kV, the rise time is roughly one microsecond, which can only increase with the output voltage.
FR-A-2 638 304 discloses high voltage, pulse generators comprising coaxial cables charged in parallel by a high voltage source and discharged in series across switches. If T is the transit time in a cable with n cables and the charging voltage V, a voltage having an amplitude of nV/2 for duration 2T is obtained.
Although satisfactory in certain respects, these related art generators suffer from disadvantages. For example, their voltage is limited to a few dozen kilovolts and are also limited in current. This is, on the one hand due to the use of switches of the transistor, thyristor (and similar types) and, on the other hand, to the use of resistors positioned between the output line and the earth or ground and which are exposed to the high voltage supplied.